That test will work on any common ground amplifier, as the two grounds will be identical!!!
If the amplifier is common ground and so not directly bridgable, then you can just invert one of the input signals (RCA) with an inverting opamp circuit and wire across both the +ve terminals. Remember when bridging an amplifier, it reduces the minimium impediance you can drive into. For example if the stereo amplifier can drive 100W in to 4 Ohm/ch then bridged it will supply 200W in to 8 Ohm/ch.